Normally, when you think about what order moves go in when battling, you just think it is dependant on your Pokémon and your opponent Pokémon's speed. This is true, however there are several attacks which alter the progression of the attacks. Each attack has a specific hidden value called the Speed Priority. Almost all of the attacks in the game have got a Speed Priority of 0, however there are over a dozen attacks that manipulate this value in order to utilise it going first or maybe even last.

There are 13 different stages within the speed priority area from +5 all the way down to -7. Logically, as you would expect, the attacks with the highest value go first. If the two Pokémon both use an attack with say a speed priority value of 4, then the speed stat of each Pokémon comes back into play and the order is determined from there. There's also the fact that several attacks will allow use of another attack such as Assist, Metronome and so on, these will remain with a speed priority of 0. So if you were to use Metronome and you get the attack Aqua Jet while your opponent uses Fake Out, both of which have a priority of 1, Fake Out will still go first, regardless of the speed.

Switching pretty much always happens first, before any attacks. However, there is one attack that has a varying speed priority value; Pursuit. Normally it has a value of 0, but if your opponent switches just as you have selected Pursuit, Pursuit will always hit before the Pokémon switches out. Moves which utilise switching out such as Baton Pass or U-Turn however keep their priority value of 0 and so can still be hit before. In Rotation Battles however, the rotation occurs straight away at the start of the turn and bypasses any and all moves.

There are also several items that mess with the speed priority. Quick Claw is the most common one you will see. It has a 3/16 chance of boosting your Pokémon's priority and attacking first. However, this is not utilised in skipping priority stages. So if you have a Quick Claw attached and it activates while you use Flamethrower, but your opponent uses Quick Attack, you will still attack second. There are items such as Full Incense and the Lagging Tail which do the complete inverse of this and make you last within that Speed Priorit, but as with the Quick Claw, if you use Flamethrower but your opponent uses Avalanche, you will move first. These items also completely ignore the effect of Trick Room.

Trick Room is a unique attack in that it inverses the speed of the users so the faster Pokémon go last, while the slower Pokémon will go first. The speed priority stages still remain the same however so Quick Attack will still hit before Flamethrower. The aforementioned items are exempt from this however.

In Pokémon Black & White, a new ability, Prankster, is introduced. This ability increases the Speed Priority of all non-attacking moves by 1 stage for the Pokémon with the ability. This means that all standard moves, normally within the Stage 0 band, will act as if they were in the Stage 1 band and so forth. Pokémon X & Y went further with the new abilities and introduced the ability Gale Wings, which increases the Speed Priority of all Flying-type moves known by the Pokémon with that ability by one.

Mega Evolution has a Speed Priority beyond Stage 5, and will always occur at the start of battle before anyone attacks or switches. However, due to this, any changes in the Speed Priority brought by a new ability, such as Banette mega evolving and gaining the ability Prankster, are not factored in within the turn of Mega Evolution but will be in all subsequent turns.